1. Field of the Invention
The present invention relates to a technology for analyzing a panorama image.
2. Description of the Related Art
For map maintenance to keep map data updated, roadside information, such as a change in store information, is commonly collected by taking roadside pictures on the scene to be examined later, instead of walking around the scene for field survey.
Such roadside pictures are, however, usually data (moving picture) of long hours. Therefore, to check the pictures to analyze the information, it requires a great deal of labor. With such reason, another method of creating a roadside panorama image (still image) to be used in the analysis has been employed.
A roadside panorama image is created by projecting picture frames including two-dimensional images accumulated in the direction of the time axis onto a single two-dimensional image without the time axis. With such panorama image, it is possible to easily and intuitively understand the overall situation of a roadside. Therefore, a load of checking the pictures to collect the information can be reduced.
Moreover, the roadside pictures taken while moving on a road include, for example, images of the same roadside part if an image-capturing device stops at a traffic light. In contrast, the roadside panorama image created along the horizontal axis of travel distance instead of the time axis reduces the repeatedly captured same roadside part images into the same image to prevent the same subject from appearing in the panorama image multiple times. The roadside panorama image, therefore, reduces the volume of data remarkably, compared to the roadside pictures.
A method of creating a roadside panorama image is disclosed in, for example, Japanese Patent No. 3230998. This method is employed principally for detecting a perking vehicle or inspecting the interior of a tunnel. According to the method, slits are taken using a line sensor mounted on a vehicle, while measuring the travel distance or travel speed of a mobile object precisely to adjust timing of shooting, and the slits are connected laterally to form a roadside panorama image.
Another method is disclosed in for example, Japanese patent Laid-Open Publication No. H11-164325. In this method, pictures taken by a video camera mounted on a vehicle is used to create the panorama image. Parts of each picture frame (slit image) are cut out and connected to form a panorama image. According to this method, each optical flow on the vertical centerline of an image in each picture frame is calculated, and a width (referred to as basic flow) based on each optical flow is determined. According to the determined width, the vicinity to the centerline of the image is cut out in a shape of a vertically elongated strip as a slit image. In this manner, the slit image is cut out from each picture image, and each slit image is connected to adjacent one in order.
A part containing optical flows smaller than the cutout width, i.e., the basic flow, may be stretched properly upon cutting out. A panorama image created by the above methods is easier in checking than the moving picture, however, sometimes becomes a laterally elongated image that contains tens of thousands of pixels sideways.
In analyzing a roadside, although reduction of trouble in checking images has been tried by a use of the roadside panorama image as the conventional techniques described above, the roadside panorama image is required to be checked. Therefore, a load on the worker engaged in the map maintenance work has still been heavy.
Besides, a change in the roadside situation is detected by checking both the previous roadside panorama image and the present roadside panorama image by the worker. Thus, detection of the change is dependent on the worker, and the map maintenance work cannot be efficiently done.